Heretofore, there was proposed a blood collecting apparatus as described in Japanese patent publication No. Sho 51-3153.
A blood collecting apparatus, in general, must include a sensor for measuring the amount of blood collected into a blood container.
In a blood collecting apparatus for collecting blood into a blood container by negative pressure to be generated by a vacuum pump, the blood collecting apparatus must be provided with a pressure sensor for measuring pressure in a blood collecting evacuated chamber where the blood container is to be set.
(I) The measuring sensor and pressure sensor can be handled such that the output of those sensors is in a certain relationship with the measured weight (amount of collected blood or pressure), which can be expressed as a constant function. Therefore, a blood collecting apparatus is provided with control means for calculating a desired measured weight (amount of collected blood or pressure) on the assumption that the output of the measuring sensor can be expressed as the above-mentioned specific function.
Taking the sensor for measuring the amount of collected blood as representing the other, if it is handled such that the output y of the measuring sensor is in a certain relation with the measured weight w of collected blood, which can be expressed as the linear function y=aw+b (wherein a: gain [sensitivity] and b: offset value), the constants a and b are characteristics inherent to the individual sensors are thus different for each sensor from the beginning.
Therefore, in a blood collecting apparatus using a sensor as stated above, it is required that the constants are properly changed for correction in the early stage of the use of such sensor and also in the transit stage of the use thereof, so that the amount of collected blood calculated by control means based on the output of the sensor always coincides with a proper value.
At that time, it can be considered that the correction of changing the constants a and b of the sensors is effected by providing a change circuit and that the output signals of the sensor are adjusted by volume or the like. However, this idea has, for example, the following inconveniences. 1 a conversion circuit is required and 2 the volume, etc. must be adjusted in the manufacturing process and in the using process.
An object of the present invention is to correct the characteristics of a sensor for measuring the amount of collected blood with ease and to obtain accuracy in measurement of the amount of collected blood.
Another object of the invention is to correct the characteristics of a pressure sensor and to obtain accuracy in measurement of pressure generated in a blood collecting evacuated chamber.
(II) Similarly, taking the sensor for measuring the amount of collected blood as representing the other sensor, if it is handled such that the output y of the measuring sensor is in a certain relationship with the measured weight w of collected blood, which can be expressed as the linear function y=aw+b (wherein a: gain [sensitivity] and b: offset value), the offset value b sometimes drifts with the passage of time because of heat and changes in stress, as is generally characteristic of sensors (see FIG. 8).
Accordingly, when the offset value b01 of the linear function initialized in the control means should be drifted in such a way as b02, b03 . . . during the use, error values (b02-b01), (b03-b01) . . . would occur unless they are corrected.
A further object of the present invention is to normally and automatically correct the change of the offset value of the output of a sensor for measuring the amount of collected blood caused by drift and to obtain accuracy in measurement of the amount of collected blood.
A still further object of the present invention is to normally and automatically correct the change of the offset value of the output of a pressure sensor for measuring the amount of collected blood caused by drift and also to obtain accuracy in measurement of the pressure formed in blood collecting evacuated chamber.